What are tent coatings and deniers?

I’m looking for a new family tent and confused about fabric ratings. One store’s website says something about 1,000mm coatings, but I don't see any references to that on other sites. I did see one that said "70 denier." What's that and how do I compare? Robin Highland, Indiana

A:
Coatings and deniers are different things, but equally confusing. Well start with coatings. All tents have polyurethane coating on the floor and waterproof fly, and its the coating that keeps you dry, not the fabric itself. A coating of, say, 1,000mm doesnt mean the coating is that thickthat would make it nearly 40 inches thick. Instead, its a measure of how much hydrostatic pressure the coating can take before it leaks. That test is accomplished by securing a selected piece of fabric to the end of a long tube, to which water is added. The 1,000mm designation means that 1,000mm of water can be added before the coating leaks.

REI Hobitat 4

Hobitat 4

Obviously, a higher number is better, as a thin coating is less resistant to abrasion and therefore more apt to fail. For a tent floor, Id say about 1,000mm pressure resistance is the minimum for wet conditions. The fly can get away with a lower rating because youre not kneeling on it and potentially squeezing water through the fabric. High-end backpacking tents will have floor coatings rated to as much as 3,500mm.

Denier (pronounced den-YAY) is a unit of measurement that applies to a yarns thickness. Packs often have fabric with a denier of 500 or morepretty heavy stuff, for more durability (but also with big gaps between fibers, which is why its so difficult to waterproof a pack). Clothing uses much finer yarn, so the denier there is often around 70 or so. In tents youll find a mix, depending on where the fabric is used, with a denier of 75 and 150 most commonly found.

You dont say what kind of tent youre looking for. If car camping, then a good choice for a family of four is REIs new Hobitat 4 ($259; www.rei.com) or Hobitat 6 ($329). These are exceptionally sturdy tents for their size, with a rugged 300-denier floor and a coating rated to 1,500mm. I also like the Eureka! Equinox ($349; www.eurekatent.com), which sleeps six. Its floor is rated to 1,200mm.

I almost always recommend that tent users place something under the tent to protect the floor from abrasion. Most tent manufacturers will happily sell you a footprint" for $40 or more. But you can buy some light polyethylene sheeting at your local hardware store and cut yourself a piece. Make it slightly smaller than the size of the floor, so water dripping off the tent doesnt catch on the footprint and collect under the tent.

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